Jet fuel additives



United States Patent 3,258,320 JET FUEL ADDITIVES Eugene A. Kent, Argo, Ill., assignor to Nalco Chemical Company, Chicago, 11]., a corporation of Delaware No Drawing. Filed May 31, 1960, Ser. No. 32,545 4 Claims. (CI. 44-71) This application is a continuation-in-part of copending application Serial Number 694,713 which was filed on November 6, 1957, now abandoned.

The present invention relates to the treatment of jet fuels. More particularly, the invention is directed to additives for jet fuels which substantially inhibit the formation of deposits in the heat exchangers of jet engines and/ or decrease the tendency of the fuel to clog in the burner nozzles and filters of jet engines.

One of the serious problems facing designers of jetpowered aircraft concerns the removal of heat which is developed during high speed flight. Air has not proven to be a practical coolant and, therefore, designers have made use of the fuel itself to cool lubricating oil and various aircraft components such as hydraulic systems and air conditioning equipment.

The use of fuel as a heat sink has provided a convenient means of cooling various parts of the aircraft. Unfortunately, however, the use of the jet fuel for this purpose has subjected the fuel to severe degradation con ditions. The degradation or thermal instability of jet fuels is of major concern because it may adversely affect engine performance and/or the cooling function through the formation of insoluble sediment which clogs fuel passages and burner nozzles and/ or the formation of deposits on heat transfer wallsthus decreasing the heat transfer coefficient and reducing the size of the fuel passages.

Production runs of jet fuels vary considerably with respect to thermal instability. The cause of these variations among jet fuels is unknown, but it has been noted that jet fuels produced by different oil refining companies vary considerably with respect to deposits and filterability. Straight run fuels exhibit little thermal instability at present jet engine temperature requirements. Occasionally, however, straight run fuels are encountered which are borderline or unstable. The major problems of thermal instability, however, arise with jet fuels derived from cracked stock or blends of cracked stock with straight run fuels.

The term jet fuel as it is used in the instant description refers to fuels which are manufactured and marketed to serve as the fuel in jet engines. In general, these fuels are liquid hydrocarbon mixtures having boiling points in the kerosene range or blends of mixtures in the kerosene range with gasoline. The military services presently use either JP-4 jet fuel, a blend of gasoline and kerosene, or JP-5 jet fuel, a kerosene type hydrocarbon fuel. Jet engines can use a wide variety of fuels as compared to piston type aircraft engines and, hence, jet fuels are not susceptible to precise definition. In general, however, jet fuels with which the instant invention is concerned are liquid hydrocarbons having a distillation end-point not exceeding about 600 F.

It is, accordingly, an object of the present invention to provide new compositions of matter which are useful as additives for jet fuels to improve the thermal stability of the jet fuels.

Another object of the invention is to provide jet fuels containing the additives of the instant invention. Other objects will be apparent to those skilled in the art from the following detailed description.

The additives of the present invention are the reaction products obtained by reacting at elevated temperatures citric acid and tertiary-alkyl primary amines of the formula:

the amine having 11-22 carbonsthe reaction being carried out with the removal of from about 1.0 to about 3.0 and preferably from 1.25 to 1.75 mols of the water of reaction per mol of the citric acid. More specifically, the tertiary-alkyl primary amine constitutes a compound wherein R and R are lower alkyl groups, usually methyl groups, and R constitutes a long chain alkyl radical composed of 8 to 19 carbons. Tertiary-alkyl primary amines which have been found to be especially suitable for the instant invention are Primene 81-R and Primene JM-T, marketed by Rohm and Haas Company. Primene 8lR is reported by the Rohm and Haas Company to be composed of principally tertiary-alkyl primary amines having 11-14 carbons and has a molecular weight principally in the range of 171213, a specific gravity at 25 C. of 0.813, a refractive index of 1.423 at 25 C., and a neutralization equivalent of 191. Primene JM-T is reported by the manufacturer to be composed of tertiary-alkyl primary amines having 18-22 carbons with a molecular weight principally in the range of 269-325, a specific gravity at 25 C. of 0.840, a refractive index at 25 C. of 1.456, and a neutralization equivalent of 315. Of the two amines, Primene JM-T is preferred because the ultimate reaction products with citric acid have better oil solubility as compared with equivalent products made with Primene 81-R.

The reaction product which is most consistently suc cessful in the reduction of tube deposits and improvement of filterability is the reaction product of 3 mols of the tertiary-alkyl primary amines previously described with citric acid with the removal of 1.0 to 3.0 mols of water per mol of citric acid. The citric acid is preferably anhydrous, or at least substantially anhydrous. The molar ratio of amine to citric acid can vary from about 1:1 to about 3:1.

The reaction products of the instant invention may be prepared by any of several methods. They may be reacted at atmospheric pressure or under vacuum without a solvent. Alternatively, a high boiling solvent may be employed to reduce the viscosity of the ultimate product and thus facilitate agitation and mixing of the reactants. The solvent in this case has a boiling point high enough that it is not distilled off to any appreciable extent during the reaction at the prevailing pressure.

Another method of preparation involves the use of a low boiling solvent, such as toluene, which forms an azeotropic mixture with the water of reaction. The distillate is refluxed and the water separated from the low boiling solvent before the later is returned to the reaction mixture.

In all of the foregoing methods, the reactants are heated sufficiently to distill off the Water of reaction at the prevailing pressure conditions. In reactions at atmospheric pressure, the tertiary-alkyl primary amine and citric acid are mixed together in a vessel equipped with an agitator and heating means and heated to a temperature between about C. and C. for /2 to 2 /2 hoursthe time-temperature relationship depending upon the amount of water of reaction to be removed. The heating of the reactants is terminated when the desired amount of water of reaction is removed-the latter being determined by collecting and measuring the water distilled off. An alternative method for determining the end-point involves ascertaining the acid number of samples taken at periodic intervalsthe reaction being terminated when the approximate desired acid number is reached. In a preferred form of the invention, the reaction is terminated so as to obtain a product having an acid number, based on the active ingredients, preferably in the range of 65-90 where the amine is Primene JM-T. The acid number range, of course, will vary according to the particular amine used in the reaction. One preferred method at atmospheric pressure involves heating the amine to a temperature of 50 C.-60 C. and adding the citric acid slowly in increments. After all the citric acid is added the reactants are gradually heated to a temperature of 140 C.160 C. in a period of about one-half to one hour. The reaction mixture is held at this temperature for an additional 1% to 2 /2 hours. If desired, the product may be diluted with a suitable hydrocarbon solvent such as Bronoco IOOWR or xylene to the desired concentration.

In a reaction under vacuum, the amine is vigorously stirred and the citric acid is added in portions. The mixture is then rapidly heated. When the temperature is in the range of 100-120 C., a full vacuum is slowly applied. The reaction is kept at this temperature for about /2-2 hours and is then cooled rapidly to 100 C. A suitable hydrocarbon solvent is then added in an amount sufiicient to provide the required concentration.

When a high boiling solvent such as Stoddard Solvent or other commercial high boiling hydrocarbon solvent is employed, the amine and citric acid are mixed with the desired amount of solvent, and the mixture is heated with agitation in the manner previously described. The azeotropic distillation method is carried out by mixing the amine and citric acid with a low boiling solvent such as toluene in :a reaction vessel equipped with an agitator, condenser, and Barrett trap for separating the water and solvent in the azeotropic distillate and the mixture is heated with agitation. The solvent begins to reflux, and refluxing is continued with the removal of water from the azeotropic distillate until the desired amount of water is removed.

The invention will be further understood from the following specific examples and it will be understood that the invention is not limited thereto.

The first five examples describe the preparation of certain of the subject additives.

EXAMPLE I Three (3) mols of Primene JMT and 1 mol of citric acid, along with 368 grams of Stoddard solvent, are added to a reaction vessel equipped with an agitator, thermometer, Barrett trap and condenser. The mixture is heated until the temperature reaches 120 C. at which point a vacuum is applied. Distillation begins, and about 3 milliliters of the solvent is distilled over and collected. The temperature of the reaction mixture continues to rise and at about 126 C., the distillation becomes more vigorous. The temperature remains constant thereafter at about 124-126 C. During the reaction period, the temperature rises to about 145 C., and the reaction is stopped when 25.2 milliliters of Water have distilled over. This amount of water is equivalent to 1.4 mols of water per mol of citric acid.

EXAMPLE II Primene JM-T and citric acid are reacted at a molar ratio of 3:1, respectively, in a vessel identical with that described in Example I. The reaction mixture is heated and agitated and at 120 C. a vacuum is applied. After a few minutes, distillation of the water begins. As the reaction proceeds, the reaction mixture begins to darken. Heating is continued until the temperature is in the range of 140150 C. The reaction is continued until about 1.8 mols of water per mol of citric acid are removed. Thereafter the heating is discontinued and the reaction product is diluted with a suitable hydrocarbon solvent to the desired concentration.

l EXAMPLE III Three (3) mols of Primene JM-T are added to an open vessel, and the amine is heated to a temperature between 50 and 60 C. One (1) mol of citric acid is added portionwise to the amine. After all of the acid is added, the temperature is raised and held within the range of 150160 C. The product begins to darken at this temperature and after 2 /2 hours, an acid number is taken and found to be about 85. The reaction is then stopped and the product was made up into a 75% solution in R-381 hydrocarbon solvent and filtered through a filter cell.

EXAMPLE IV Equal mols of Primene 81-R and citric acid are mixed with an amount of toluene equal to about twice the total Weight of the amine and acid in a reaction vessel identical with that described in Example I. The mixture is stirred and heated. At about C., the toluenebegins to reflux and when the water in the azeotropic distillate is removed the color of the reaction mixture changes from a light yellow to a dark brown as the reaction nears completion. After three hours of refluxing about 1.8 mols of water per mol of citric acid have been removed and no further distillation of water is noted. The temperature at this point is about 112 C. and the reaction is stopped.

EXAMPLE V In an apparatus identical with that of Example I, Primene 81-R and citric acid at a molar ratio of 3:1, respectively, are mixed with an amount of toluene approximately equal to the total weight of the amine and acid. The reaction mixture is heated and stirred. At about 110 C. the toluene begins to reflux and the water is removed from the azeotropic distillate. When 1 mol of water per mol of the acid is removed, the reaction is stoppedthe temperature at this point being about 118 The additives, generally in diluted form in a hydrocarbon solvent, are added and mixed with a jet fuel in amounts generally within the range of 25250 p.p.m. and preferably from about 25-150 p.p.m., the concentration being calculated on the basis of the active ingredient. The quantity added for optimum results will vary between jet fuels and may even vary to some extent as a given batch of jet fuel ages. For this reason, routine tests should be carried out on each of the fuels which are to be treated in order to determine the optimum dosage. Too high a dosage will limit the improvement over untreated fuels and may even cause additional fouling.

Evaluations of thermal stability of treated jet fuels In evaluating the eifectiveness of the jet fuel additives of the instant invention, tests were conducted with an Erdco CFR Fuel Coker, manufactured by the Erdco Engineering Corporation, Addison, Illinois. The Erdco Coker is designed to evaluate thermal stability of fuels with respect to tendencies toward deposits on heat transfer walls and also with respect to tendencies toward clogging lines and burner nozzles.

In the Erdco Coker, the fuel is supplied under constant pressure to an annular chamber formed by two tubes of different diameter. The inner tube is an aluminum tube which has disposed inside thereof substantially throughout the length of the tube an electrical heating element to heat the aluminum tube. This section of the apparatus is designed to evaluate the tendencies of the heated fuel toward deposits on heat transfer surfaces. The fuel, as it flows at a constant predesignated rate of flow through the annular chamber, is heated by the aluminum tube to the designated test temperature. At the end of the test period, the aluminum. tube is removed, and the character and size of the deposits thereon are observed.

After the fuel leaves the annular chamber, it is flowed through a filter provided With electrical heating elements to measure the thermal stability of the fuel toward formation of clogging sediment. The fuel temperature is usu ally raised to a designated filter test temperature, and the pressure drop across the filter is noted as the test fuel fiow was maintained at 6 pounds per hour at a pressure of 150 pounds; the preheater temperature was 300 F. for JP-4 fuels and 400 F. for JP- fuels. The filter furnace temperature was 400 F. for JP-4 fuels and proceeds. A pressure drop in excess of Hg is con- 5 500 F. for JP-S fuels. In some instances, where the sidered to be unsatisfactory. fuel had a severe tendency to clog the filter, the filter was EXAMPLE VI removed. Tests run with the filter removed are denoted with an asterisk in the pressure drop column.

A series of evaluations were conducted in an Erdco T following m i a Summary f te t conducted C k With l J fuels 111 P Q Wlth test- 10 with various fuels. Composition A is the product of Procedure (mauled y the Coofdlnatlng Reseamh Example III. Composition B is the product of Example Council, including IIlOdificafiOIlS and changes in CRC V. The dosage reported is calculated on the basis of reports dat M y 1956, and August 1956' T e the concentration of the active ingredient.

Table I FUEL A (JP-5) Test Filter No. Treatment Dosage, Time, Pressure Condition of Preheater Tube and p.p.m. min. Drop, Remarks in. Hg

10 Irregular, circumferential, shiny, brown-black deposits, Deposit: 3%-4% in length. 1.17 85-90% reduction of deposit. 0.38 90% reduction of deposit. C) 95% reduction of deposit. 90% reduction of deposit.

FUEL B (JP-5) l Blank 37 10 2 Blank 150 Irregular, tan, circumferential deposit plus haze.

3 Comp. A--. 75 150 0.55 50% deposit reduction. Tan

streak about 3% x A5 plus small additional haze area.

4 Comp.B 200 150 0.15 98% deposit reduction. Discoloration and haze barely visible.

5 Comp. 3.... 75 150 Approx. same No. 3 above.

FUEL C (J P-4) 1 Blank 150 0.5 Irregular circumferential discoloration area about 5" long plus additional haze.

2 Comp. A. 75 150 0. 16 Slight reduction of discoloration area over blank. Test run about six weeks after blank.

FUEL D (JP-5) 1 Blank 91. 2 10 Circumferential, irregular dark tan deposit 4% to 5% long. 2 Comp. A. 150 0.21 Alglmt deposit reduction over 3 Comp. A 150 0.32 Alt))(1 utk80% deposit reduction over 4 Comp. A- 150 0.10 About deposit reduction over 5 Comp. A. 100 150 0.11 Al(1 util;75% deposit reduction over 6 Comp. A. 150 150 About 70% deposit reduction over over blank.

7 Comp. B 150 150 About 98% deposit reduction over blank.

FUEL E (JP-4) 1 Blank 150 0.69 Very light colored haze and varnish about 6% long.

2 Comp. A.-. 100 150 0.09 Barely visible discoloration (mostly haze) about 6 long.

3 Comp. A 200 150 0. 21 lean.

FUEL F (JP-5) 1 Blank 102. 7 l0 Irregular area of dark tan deposit.

2 Comp. A- 100 150 0.16 Featherlike pattern of light tan deposit% reduction over blank.

3 Comp. A- 150 150 0.21 About 80-85% deposit reduction over blank.

4 Comp. 3.... 150. Light tan depositabout 90% reduction over blank.

Table ICntinued FUEL G (JP-4) Additional evaluations of the Erdco Coker were conducted under conditions outlined above on still another JP-S fuel. The tests were run for the most part without the filter on a run of the fuel without additive. Orange brown deposits were observed on the preheater tube of the Erdco Coker. With 130 parts per million of the product of Example IV added to this fuel, an 80% reduction of tube deposits was observed, the deposits being a light varnish.

At concentrations as low as 5 parts per million, improvement in filterability was noted over the blank. Al though the pressure drop across the filter remained relatively high, the deposits on the tube were observed to be lighter in color. The filterability improved as the concentration of the additive was increased to and 30 parts per million, but appeared to decrease somewhat at 40 parts per million.

With a different JP-S fuel, the Erdco Coker deposits for a test time of 150 minutes on a blank sample were substantial and brown-black in color. In a test run with the same fuel containing 130 p.p.m. of the additive of Example IV, the Erdco Coker tube was virtually clean and provided an estimated 99% reduction in deposits.

EXAMPLE VII In this example a comparison is made between the effectiveness of the subject additives and (1) reaction products of citric acid and Primene JM-T where no water is removed, and (2) reaction products of citric acid and Primene JM-T where less than 1 mol of water is removed. In the following table, Product A is the reaction product of citric acid and Primene JM-7 (mol ratio of 1:3) with no water removed; Product B is the reaction product of citric acid and Primene JM-T (mol ratio of 1:3) where 1.39 mols of water were removed for each mol of citric acid; Product C is the reaction product of citric acid and Primene JM-T (mol ratio of 1:3) where .84 mol of water was removed for each mol of citric acid; Product D is the reaction product of citric acid and Primene JM-T (mol ratio of 1:3) where 1.07 mols of water were removed for each mol of citric acid; and Product E is the reaction product of citric acid and Primene J M-T (mol ratio of 1:3) where 1.56 mols of water were removed for each mol of citric acid.

As is evident from the chart, the removal of water during the reaction is essential if satisfactory jet fuel additives are to be obtained. It is also clear that where at least 1 mol of water wa-s removed per mol of citric acid, the condition of both the filter and the preheater was improved.

The exact chemical structure of the reaction products or the instant invention are not known and cannot be predicted with any degree of certainty. It is probable that the reaction product consists of a mixture of different compounds. It is known, however, that under the reaction conditions outlined heretofore that some of the carboxyl groups of the citric acid are reacted with the amine to form amine salt and other carboxyl groups react to form a different type of chemical bondthe latter resulting from the removal of the water of reaction.

Obviously many modifications and variations of the invention as hereinbefore'set forth may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated in the appended claims.

The invention is hereby claimed as follows:

1. A liquid hydrocarbon jet fuel containing 25-250 p.p.m. of a reaction product prepared by heating for at least /2 hour with the removal of water of reaction citric acid and a tertiary-alkyl primary amine of the formula wherein R and R are lower alkyl groups and R is an alkyl group having 8-19 carbons, the molar ratio of amine to acid in the reaction mixture being about 3:1, respectively, until 1.25-1.75 mols of water of reaction per mol of citric acid are removed from the reaction mixture.

2. A liquid hydrocarbon jet fuel containing 25-150 0 p.p.m. of a reaction product prepared by heating for at R1 Ra 1-NH2 la wherein R and R are lower alkyl groups and R is an alkyl group having 8-19 carbons, the molar ratio of amine to acid being about 3:1, respectively, until about 1.4 mols of water of reaction per mol of citric acid are removed from the reaction mixture.

3. A liquid hydrocarbon jet fuel containing 25-150 p.p.m. of a reaction product prepared by heating for at least /2 hour with the removal of water of reaction citric acid and a tertiary-alkyl primary amine of the formula wherein R and R are lower alkyl groups and R is an alkyl group having 15-19 carbons, the molar ratio of amine to acid being about 3:1, respectively, until 1.25- 1.75 mols of water of reaction per mol of citric acid are removed from the reaction mixture.

4. A liquid hydrocarbon jet fuel containing a stabilizing amount of a condensation reaction product prepared by heating for at least /2 hour with removal of water of reaction citric with tertiary-alkyl primary amines of the formula 10 having 18-22 carbons and wherein R 'and R are lower molecular weight alkyl groups and R is a higher molecular weight alkyl group, the molar ratio of said amine to citric acid'in the reaction mixture being about 3:1, respectively, until said reaction product has an acid number, on a 100% active basis, in the range of about 6590.

References Cited by the Examiner UNITED STATES PATENTS DANIEL E. WYMAN, Primary Examiner.

LEON D. ROSDOL, JULIUS GR-EENWALD,

Examiners.

Y. M. HARRIS, J. E. DEMPSEY, Assistant Examiners. 

1. A LIQUID HYDROCARBON JET FUEL CONTAINING 25-250 P.P.M. OF A REACTION PRODUCT PREPARED BY HEATING FOR AT LEAST 1/2 HOUR WITH THE REMOVAL OF WATER OF REACTION CITRIC ACID AND A TERTIARY-ALKYL PRIMARY AMINE OF THE FORMULA 